Contaminate removal using aluminum-doped magnetic nanoparticles

ABSTRACT

Exemplary embodiments of the present invention can include a method for isolating a contaminate from water comprising: introducing a plurality of aluminum-doped nanoparticles to water, the water comprising the contaminate; contacting the plurality of aluminum-doped nanoparticles with the contaminate to form contaminate-adsorbed nanoparticles; and isolating the contaminate-adsorbed nanoparticles by applying a magnetic field to the water.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/612,667 filed 2 Jun. 2017, which claims the benefit of U.S.Provisional Patent Application No. 62/345,482, filed 3 Jun. 2016, theentire contents and substance of which are hereby incorporated byreference as if fully set forth below.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

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SEQUENCE LISTING

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STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINTINVENTOR

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BACKGROUND OF THE INVENTION

Limited supply of phosphorus (P) reserves and the increasing demand forfood production have created a strong demand for P fertilizers. Global Pdepletion is one of the important challenges in the 21^(st) century.However, runoff from fields and feedlots introduces large quantities ofP-containing fertilizers and animal wastes into surface waters, causingwater pollution and eutrophication. Such runoff is a danger for thedenizen of water and the whole ecosystem on a broader prospective.Eutrophication caused by municipal and industrial wastewaters wasreported even at low concentrations of P (less than 1 mg/L). In order tocontrol algal growth, the U.S. EPA water quality criteria stated thatphosphate should not exceed 0.05 mg/L for streams discharging into lakesor reservoirs, 0.025 mg/L within a lake or reservoir, and 0.1 mg/L forstreams or flowing waters not discharging into lakes or reservoirs.Improved management strategies and treatment technologies are highlydesired in order to reduce agricultural runoff and to capture andrecycle P before it reaches waterbodies.

Many approaches have been developed to remove dissolved phosphate fromwastewaters prior to their discharge into natural water bodies andrunoff, including physical, chemical, and biological treatment methods.Typically, phosphate is separated from wastewaters by adding Al—, Fe—,or Ca-based coagulants and allowing the precipitates to settle out. Acommon drawback of this coagulation process is the high costs associatedwith the use of metal salts and the treatment of the remaining sludge.

The enhanced biological phosphorus removal (EBPR) process utilizespolyphosphate-accumulating organisms (PAO) to take up and polymerizeinorganic phosphate to produce polyphosphate (polyP). P level of lowerthan 0.11 mg/L can be achieved in the effluents after the EBPR treatmentof municipal wastewater. However, the performance of EBPR can bedramatically reduced due to many environmental and operating factors,making this process unstable. In addition, the inability to isolate theresponsible microorganisms in EBPR and to verify their biochemicalmetabolism appeared to limit the development of a better understandingof the operating metabolic pathways and the characterization of theentire microbial ecology of the systems, thus hampering furtherimprovement of the EBPR system.

Adsorption has attracted increasing interests for phosphate removal fromwastewater due to the easiness of design and operation and no additionalproduction of sludge. This method has also been considered as aneffective approach for recycling P from wastewater effluents. Over thepast decade, various adsorbents have been developed for phosphateremoval from wastewaters including agricultural waste and by-products,anion-exchange resins, iron-oxide based adsorbents, aluminum-containingmaterials, and layered double hydroxides. However, additional filtrationor centrifugation steps are likely needed for the separation of sorbentsfrom aqueous solutions.

Magnetic nanomaterial-based sorbents are very attractive due to theirhigh surface area and facile solid-liquid separation under an appliedmagnetic field. Their surface areas per unit volume can be on the orderof 5×10⁷ m²/m³ for a 10% dispersion of 15-nm particles. Adsorption ofphosphate onto amine functionalized magnetic nanoparticles throughelectrostatic attraction has been reported. However, the simpleelectrostatic adsorption might suffer from the interference ofco-existing anions in wastewater. Core shell materials with Fe₃O₄ as thecore (˜600 nm diameter) and ZrO₂ as shell (˜10 nm thickness) have alsobeen used to remove phosphate, with adsorption capacities ranging from 8to 39 mg P/g.

BRIEF SUMMARY OF THE INVENTION

In an exemplary embodiment, the present invention is a method comprisingforming contaminate-adsorbed nanoparticles from dispersion ofaluminum-doped nanoparticles and a contaminate, and applying a magneticfield to at least a portion of the contaminate-adsorbed nanoparticles.

The aluminum-doped nanoparticles can be synthesized from a mixture offerric salt, ferrous salt, and aluminum salt with sodium hydroxide.

The aluminum-doped nanoparticles can be characterized by a maximumcontaminate adsorption capacity of greater than 50 mg/g based on theLangmuir model.

The method can further comprise introducing the aluminum-dopednanoparticles to a fluid comprising the contaminate, wherein forming thecontaminate-adsorbed nanoparticles comprises dispersing at least aportion of the aluminum-doped nanoparticles in the fluid, and whereinapplying the magnetic field comprises applying the magnetic field to thefluid, which segregates at least a portion of the contaminate-adsorbednanoparticles.

The contaminate can be selected from the group consisting of biochemicaloxygen demand (BOD), chemical oxygen demand (COD), total suspendedsolids (TSS), total dissolved solids (TDS), fat-oil-grease (FOG), totalKjeldahl nitrogen (TKN), total phosphates (TP), a phosphorus species,suspended solids, dissolved solids, a fat, an oil, a grease, and acombination thereof.

The aluminum-doped nanoparticles can be synthesized from a mixture offerric salt, ferrous salt, and aluminum salt with sodium hydroxide, andthe aluminum-doped nanoparticles can be characterized by a maximumcontaminate adsorption capacity of greater than 50 mg/g based on theLangmuir model.

In an exemplary embodiment, the present invention is a method comprisingforming contaminate-adsorbed nanoparticles by introducing aluminum-dopednanoparticles to a contaminate selected from the group consisting ofbiochemical oxygen demand (BOD), chemical oxygen demand (COD), totalsuspended solids (TSS), total dissolved solids (TDS), fat-oil-grease(FOG), total Kjeldahl nitrogen (TKN), total phosphates (TP), aphosphorus species, suspended solids, dissolved solids, a fat, an oil, agrease, and a combination thereof, and isolating at least a portion ofthe contaminate-adsorbed nanoparticles by applying a magnetic field tothe contaminate-adsorbed nanoparticles, wherein the aluminum-dopednanoparticles are characterized by a maximum contaminate adsorptioncapacity of greater than 50 mg/g based on the Langmuir model.

Forming contaminate-adsorbed nanoparticles can comprise introducing thealuminum-doped nanoparticles to a fluid comprising the contaminate.

An isolation efficiency of the contaminate-adsorbed nanoparticles can bepH-independent in the range of the fluid pH from 4 to 9.

The contaminate can be a phosphorus species, and the aluminum-dopednanoparticles can be characterized by a maximum contaminate adsorptioncapacity of greater than 81 mg/g based on the Langmuir model.

The contaminate can be a phosphorus species, and the aluminum-dopednanoparticles can be characterized by a maximum contaminate adsorptioncapacity of greater than 102 mg/g based on the Langmuir model.

The method can further comprise removing at least a portion of theisolated contaminate-adsorbed nanoparticles from the fluid.

The containment concentration of the fluid after removal of at least aportion of the contaminate-adsorbed nanoparticles can be from about 40%to about 97% less than a containment concentration of the fluid prior toforming the contaminate-adsorbed nanoparticles.

In an exemplary embodiment, the present invention is analuminum-phosphorus magnetic nanoparticles produced by the processcomprising dissolving stoichiometric amounts of ferric salt, ferroussalt, and aluminum salt with sodium hydroxide in a fluid to form asolution, increasing the pH of the solution until precipitation ofaluminum-doped magnetic nanoparticles, and mixing the aluminum-dopedmagnetic nanoparticles with a phosphorus species mixture.

The phosphorus species mixture can facilitate adsorption of thephosphorus species to a surface of the aluminum-doped magneticnanoparticles, forming the aluminum-phosphorus magnetic nanoparticles,and the phosphorus species can be particulate phosphorus or solublephosphorus.

The process can further comprise heating the solution prior toincreasing the pH of the solution, and heating the solution duringincreasing the pH of the solution.

The ferric salt, ferrous salt, and aluminum salt can comprise Al₂(SO₄)₃,FeCl₃, and FeCl₂, increasing the pH of the solution can compriseincreasing the pH of the solution with the addition of NaOH, and thealuminum-doped nanoparticles can comprise 20 to 50% aluminum.

In another exemplary embodiment, the present invention is a method forremoving phosphorus species from wastewater comprising introducingaluminum-phosphorus magnetic nanoparticles to wastewater having apre-removal concentration of phosphorus species, the aluminum-phosphorusmagnetic nanoparticles configured to adsorb at least a portion of thephosphorus species and form phosphorus-adsorbed nanoparticles,subjecting at least a portion of the phosphorus-adsorbed nanoparticlesto a magnetic field, removing at least a portion of thephosphorus-adsorbed nanoparticles subjected to the magnetic field, andregenerating at least a portion of the removed phosphorus-adsorbednanoparticles by precipitating them with a regeneration agent.

Regenerating can comprise contacting at least a portion of the removedphosphorus-adsorbed nanoparticles with aluminum sulfate.

The aluminum-phosphorus magnetic nanoparticles can be characterized by amaximum contaminate adsorption capacity of greater than 50 mg/g based onthe Langmuir model.

In another exemplary embodiment, the present invention is a methodcomprising introducing aluminum-doped nanoparticles to a fluidcomprising water and a contaminate, contacting at least a portion of thealuminum-doped nanoparticles with at least a portion of the contaminateto form contaminate-adsorbed nanoparticles, and isolating at least aportion of the contaminate-adsorbed nanoparticles by applying a magneticfield to the fluid, wherein the aluminum-doped nanoparticles arecharacterized by a maximum contaminate adsorption capacity of greaterthan 50 mg/g based on the Langmuir model.

An isolation efficiency of the contaminate-adsorbed nanoparticles can bepH-independent in the range of the fluid pH from 4 to 9.

The contaminate can be selected from the group consisting of aphosphorus species, chemical oxygen demand, suspended solids, dissolvedsolids, a fat, an oil, a grease, and a combination thereof.

The contaminate can be a phosphorus species, and the aluminum-dopednanoparticles can be characterized by a maximum contaminate adsorptioncapacity of greater than 81 mg/g based on the Langmuir model.

The contaminate can be a phosphorus species, and the aluminum-dopednanoparticles can be characterized by a maximum contaminate adsorptioncapacity of greater than 102 mg/g based on the Langmuir model.

The method can further comprise removing at least a portion of thecontaminate-adsorbed nanoparticles from the fluid, wherein a containmentconcentration of the fluid after removal of at least a portion of thecontaminate-adsorbed nanoparticles is from about 40% to about 97% lessthan a containment concentration of the fluid prior to forming thecontaminate-adsorbed nanoparticles.

The method can further comprise synthesizing the aluminum-dopednanoparticles prior to introducing the aluminum-doped nanoparticles tothe fluid, wherein the aluminum-doped nanoparticles are synthesized froma mixture of ferric salt, ferrous salt, and aluminum salt with sodiumhydroxide.

The aluminum-doped nanoparticles can comprise 20 to 50% aluminum.

The method can further comprise regenerating at least a portion of thealuminum-doped nanoparticles.

Regenerating can comprise contacting at least a portion of thecontaminate-adsorbed nanoparticles with aluminum sulfate.

The aluminum-doped nanoparticles can be characterized by a maximumcontaminate adsorption capacity of greater than about 102 mg/g based onthe Langmuir model.

In another exemplary embodiment, the present invention is a method forremoving phosphorus species from wastewater comprising introducingaluminum-doped nanoparticles to wastewater having a pre-removalconcentration of phosphorus species, the aluminum-doped nanoparticlesconfigured to adsorb at least a portion of the phosphorus species andform phosphorus-adsorbed nanoparticles, removing at least a portion ofthe phosphorus-adsorbed nanoparticles by subjecting at least a portionof the phosphorus-adsorbed nanoparticles to a magnetic field, andregenerating at least a portion of the phosphorus-adsorbed nanoparticlesby precipitating them with a regeneration agent, wherein a post-removalconcentration of phosphorus species of the wastewater after removal ofat least a portion of the phosphorus-adsorbed nanoparticles is frombetween about 80 and about 95% less than the pre-removal concentrationof the phosphorus species of the wastewater, and wherein thealuminum-doped nanoparticles are characterized by a maximum contaminateadsorption capacity of greater than 50 mg/g based on the Langmuir model.

A removal efficiency of the phosphorus-adsorbed nanoparticles can bepH-independent in the range of the wastewater pH from 4 to 9.

The phosphorus species can be selected from the group consisting of anorganophosphate, a polyphosphate, and a reactive phosphate.

The method can further comprise synthesizing the aluminum-dopednanoparticles prior to introducing the aluminum-doped nanoparticles tothe wastewater, wherein the aluminum-doped nanoparticles are synthesizedfrom a mixture of ferric salt, ferrous salt, and aluminum salt withsodium hydroxide, and wherein the aluminum-doped nanoparticles aresynthesized from a mixture of ferric salt, ferrous salt, and aluminumsalt with sodium hydroxide.

The aluminum-doped nanoparticles can comprise about 20 to 50% aluminum.

The regeneration agent can be aluminum sulfate.

In another exemplary embodiment, the present invention is analuminum-phosphorus magnetic nanoparticles produced by the processcomprising dissolving stoichiometric amounts of Al₂(SO₄)₃, FeCl₃, andFeCl₂ in a fluid to form a solution, increasing the pH of the solutionwith the addition of NaOH until precipitation of aluminum-doped magneticnanoparticles, contacting the aluminum-doped magnetic nanoparticles witha phosphorus species mixture facilitating adsorption of the phosphorusspecies to a surface of the aluminum-doped magnetic nanoparticlesforming aluminum-phosphorus magnetic nanoparticles, and isolating thealuminum-phosphorus magnetic nanoparticles by applying a magnetic fieldto the mixture.

The phosphorus species can be particulate phosphorus or solublephosphorus, and the fluid can be deionized water.

The process can further comprise heating the solution prior toincreasing the pH of the solution, and heating the solution during theaddition of NaOH.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 illustrates an exemplary method 100 for contaminate removal usingaluminum-doped nanoparticles (Al-MNPs), in accordance with one or moreexemplary embodiments of the present invention.

FIG. 2 shows X-ray diffraction patterns of pure and Al-doped magnetite,in accordance with one or more exemplary embodiments of the presentinvention.

FIG. 3 is an SEM picture of prepared Al-MNPs, in accordance with one ormore exemplary embodiments of the present invention.

FIG. 4 is a high-resolution transmission electron microscopic photographof an Al-MNP particle (left) and EDX mapping of Fe and Al distributionon the particle (left), in accordance with one or more exemplaryembodiments of the present invention.

FIG. 5 shows magnetic moment measurements for pure and Al-doped MNPs, inaccordance with one or more exemplary embodiments of the presentinvention.

FIG. 6 illustrates the effect of contact time on phosphate removal, inaccordance with one or more exemplary embodiments of the presentinvention.

FIG. 7 illustrates pseudo second order fitting of phosphate removaldata, in accordance with one or more exemplary embodiments of thepresent invention.

FIG. 8 illustrates the effect of pH on phosphate removal, in accordancewith one or more exemplary embodiments of the present invention.

FIG. 9 illustrates the effect of co-existence of other anions onphosphate removal, in accordance with one or more exemplary embodimentsof the present invention.

FIG. 10 shows the P K-edge XANES spectra of phosphate sorbed pure MNPand Al-MNP, as well as reference compounds AlPO₄ and FePO₄, inaccordance with one or more exemplary embodiments of the presentinvention.

FIG. 11 illustrates percent phosphate removal with 3 mg of Al-MNP wereregenerated and reused 11 times in 10 ml of water with 10 ppm ofphosphate, in accordance with one or more exemplary embodiments of thepresent invention.

FIG. 12 illustrates the poultry wastewater treatment process, inaccordance with one or more exemplary embodiments of the presentinvention.

FIG. 13 summarizes the testing methods to be used to characterize Pspecies in liquid streams, in accordance with one or more exemplaryembodiments of the present invention.

FIG. 14 shows x-ray diffraction patterns of pure and Al-doped magnetite,in accordance with one or more exemplary embodiments of the presentinvention.

FIG. 15 shows magnetic moment measurements for pure and Al-MNPs, inaccordance with one or more exemplary embodiments of the presentinvention.

FIG. 16 illustrates the distribution and comparison of P species inwastewater before and after Al-MNP treatment for the samples collectedat different stages of wastewater treatment, in accordance with one ormore exemplary embodiments of the present invention.

FIG. 17 illustrates the percentage distribution of each P species inwastewaters before and after Al-MNP treatment for samples collected atthe different stages of wastewater treatment, in accordance with one ormore exemplary embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Although preferred embodiments of the disclosure are explained indetail, it is to be understood that other embodiments are contemplated.Accordingly, it is not intended that the disclosure is limited in itsscope to the details of construction and arrangement of components setforth in the following description or illustrated in the drawings. Thedisclosure is capable of other embodiments and of being practiced orcarried out in various ways. Also, in describing the preferredembodiments, specific terminology will be resorted to for the sake ofclarity.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise.

Also, in describing the preferred embodiments, terminology will beresorted to for the sake of clarity. It is intended that each termcontemplates its broadest meaning as understood by those skilled in theart and includes all technical equivalents which operate in a similarmanner to accomplish a similar purpose.

Ranges can be expressed herein as from “about” or “approximately” oneparticular value and/or to “about” or “approximately” another particularvalue. When such a range is expressed, another embodiment includes fromthe one particular value and/or to the other particular value.

By “comprising” or “including” is meant that at least the namedcompound, element, particle, or method step is present in thecomposition or article or method, but does not exclude the presence ofother compounds, materials, particles, method steps, even if the othersuch compounds, material, particles, method steps have the same functionas what is named.

It is also to be understood that the mention of one or more method stepsdoes not preclude the presence of additional method steps or interveningmethod steps between those steps expressly identified. Similarly, it isalso to be understood that the mention of one or more components in adevice or system does not preclude the presence of additional componentsor intervening components between those components expressly identified.

The disclosed Al-MNPs are a unique and inexpensive sorbent forcontaminate removal from water. Al-MNPs are advantageous for removingcontaminates from water because Al-MNPs have large surface areas foradsorption, do not create by-product sludge, do not require chemicals,are easily separated, and are low-cost and sustainable. Additionally,Al-MNPs can provide fast and efficient P removal from meat-processingwastewater, such as poultry wastewater, and the like.

FIG. 1 illustrates an exemplary method 100 for contaminate removal usingAl-MNPs. As illustrated at FIG. 1 , a method 100 for contaminate removalcan comprise introducing a plurality of Al-MNPs to water 110, the watercomprising the contaminate; contacting the plurality of Al-MNPs with thecontaminate to form contaminate-adsorbed nanoparticles 120; andisolating the contaminate-adsorbed nanoparticles by applying a magneticfield to the water 130. In some exemplary embodiments, thecontaminate-adsorbed nanoparticles can be removed from the water.Additionally, in some exemplary embodiments, at least a portion of theplurality of Al-MNPs can be regenerated and reused in further methodsfor contaminate removal.

In some exemplary embodiments, the contaminate can be a phosphorusspecies. For instance, phosphorus species can include but is not limitedto organophosphates, reactive phosphates, or polyphosphates.Organophosphorus can include phosphorus species derived from biologicalmatter including but not limited to DNA, RNA, and bacteria. Reactivephosphorus can include inorganic orthophosphates. Polyphosphates arecondensed phosphates including pyro, meta and polyphosphate.

In some exemplary embodiments, the phosphorus species can include bothparticulate and soluble phosphates. For instance, the phosphorus speciesmay be total acid hydrolysable phosphorus, total reactive phosphorus, ortotal organic phosphorus. In other exemplary embodiments, the phosphorusspecies can include soluble phosphates. For instance, the phosphates maybe soluble reactive phosphorus, soluble acid-hydrolysable phosphorus, orsoluble organic phosphorus.

In other exemplary embodiments, the contaminates can comprisebiochemical oxygen demand, chemical oxygen demand, total suspendedsolids, total Kjeldahl nitrogen, fat, oil, grease, and total dissolvedsolids. In an embodiment, the wastewater can comprise one or morecontaminates. In an embodiment, the contaminate can be selected from thegroup consisting of biochemical oxygen demand, chemical oxygen demand, asuspended solid, total Kjeldahl nitrogen, a fat, an oil, a grease, and adissolved solid.

Chemical oxygen demand (COD) can include a measure of the capacity ofwater to consume oxygen during the decomposition of organic matter andthe oxidation of inorganic chemicals. COD can be measured by any methodknown in the art including the introduction of a digestion reagent towater and detecting the amount of chemical oxygen demand reagentremaining in the water.

Biochemical oxygen demand (BOD) can include a measure of the amount ofdissolved oxygen that is present in water in order for microorganisms todecompose the organic matter in water. BOD can be measured by any methodknown in the art including dilution methods and manometric methods. Inexemplary embodiments where BOD is measured using a dilution method,dissolved oxygen concentrations can be measured before and afterincubation.

Total Kjeldahl nitrogen (TKN) can include a measure of the totalconcentration of organic nitrogen in water. In some exemplaryembodiments, TKN can be oxidizing inorganic and organic nitrogen bydigestion with peroxodisulfate and calculating the difference in nitratebefore and after the digestion.

Total suspended solids (TSS) can include solids in water that can betrapped by a filter. TSS can be measured by filtering a volume of waterand measuring the weight of the residue on the filter after trying.Total dissolved solids (TDS) can include inorganic salts and smallamounts of organic matter that are dissolved in water. TDS can bemeasured by filtering a volume of water, evaporating the filtrate, andweighing the remaining residue.

Fats, oils, and grease (or FOG) can be measured gravimetrically byextracting a water sample with multiple aliquots of hexane followed bythe evaporation of all of the solvent.

In some exemplary embodiments, the Al-NMPs can remove each type ofcontaminate present in the water. In some exemplary embodiments, theAl-NMPs can remove at least one type of contaminate present in thewater. As such, in some exemplary embodiments, the water can bewastewater including wastewater from a meat processing plant, industrialwastewater, municipal wastewater, and field and feedlot wastewater.

The described Al-MNPs can be configured to remove a variety ofcontaminates from water. Additionally, the Al-MNPs can be configured toremove the contaminates in varying amounts. In some exemplaryembodiments, about 40% to about 97% of the contaminate can be removedfrom the water. In some exemplary embodiments about 45% to about 97%,about 50% to about 97%, about 55% to about 97%, about 60% to about 97%,about 65% to about 97%, about 70% to about 97%, about 75% to about 97%,about 80% to about 97%, about 80% to about 95%, about 85% to about 97%,about 90% to about 97%, and about 95% to about 97% of the contaminatecan be removed. In some exemplary embodiments, up to about 99% ofcontaminate can be removed. The amount of contaminate removed from thewater as described herein can be amount of total contaminates removedfrom the water. Alternatively, the amount of contaminate removed fromthe water as described herein can be the amount of an individualcontaminate removed from the water.

The Al-MNPs can be synthesized by a variety of methods. In someexemplary embodiments, the Al-MNPs can be synthesized from a solution offerrous chloride (FeCl₂), ferric chloride (FeCl₃), and aluminum sulfate(Al₂(SO₄)₃) in deionized water. The solution can then be heated to about80° C. with NaOH for 10 minutes. In other exemplary embodiments, asolution of FeCl₂, FeCl₃, and Al₂(SO₄)₃ in deionized water can be heatedto about 90° C. Following, NH₄OH can be added, and the mixture can berefluxed for about two hours.

The Al-MNPs can comprise varying amounts of aluminum. For instance, insome exemplary embodiments, the Al-MNPs can comprise about 10% to about50% aluminum, about 20% to about 50% aluminum, about 20% to about 40%aluminum, about 20% to about 30% aluminum, about 20% to about 25%aluminum. In some exemplary embodiments, the Al-MNPs can comprise about10%, about 15%, about 20%, about 25%, about 30%, about 33%, about 35%,about 40%, about 45%, and about 50% aluminum. In some exemplaryembodiments the Al-MNPs can comprise less than about 50% aluminum, lessthan about 40% aluminum, less than about 30% aluminum, less than about20% aluminum, and less than about 10% aluminum.

When the Al-MNPs are introduced to the water containing the contaminate,the Al-MNPs can contact the contaminate to form contaminate-adsorbednanoparticles. In other words, the contaminate can adsorb to the surfaceof the Al-MNPs. The described methods are advantageous as they not onlyreduce the costs of removing contaminates from water but also becausethey show significantly improved adsorption capacity. For instance, inexemplary embodiments for removal of phosphates, the described Al-MNPscan be characterized by a maximum adsorption capacity of about 588 mg/g.In some exemplary embodiments, the adsorption capacity of the Al-MNPscan be about 100 to about 600 mg/g, about 200 to about 600 mg/g, about300 to about 600 mg/g, about 400 to about 600 mg/g, about 500 to about600 mg/g, 50 to about 105 mg/g, about 50 to about 135 mg/g, about 50 toabout 135 mg/g, about 50 to about 75 mg/g, about 50 to about 60 mg/g,about 75 to about 135 mg/g, about 80 to about 135 mg/g, about 90 toabout 105 mg/g, and about 100 to about 135 mg/g, 110 to about 135 mg/g,115 to about 135 mg/g, about 120 to about 135 mg/g, about 130 to about135 mg/g. The adsorption capacity of the Al-MNPs can be less than about600 mg/g, less than about 588 mg/g, less than about 550 mg/g, less thanabout 500 mg/g, less than about 400 mg/g, less than about 300 mg/g, lessthan about 200 mg/g, less than about 150 mg/g, less than about 132 mg/g,less than about 105 mg/g, less than about 100 mg/g, less than about 90mg/g, less than about 80 mg/g, less than about 70 mg/g, and less thanabout 60 mg/g. In some exemplary embodiments, the adsorption capacity ofthe Al-MNPs can be about 50 mg/g, about 60 mg/g, about 70 mg/g, about 80mg/g, about 90 mg/g, about 100 mg/g, about 101 mg/g, about 102 mg/g,about 103 mg/g, about 132 mg/g, about 200 mg/g, about 300 mg/g, about400 mg/g about 500 mg/g, about 588 mg/g.

The Al-MNPs can be magnetized such that after adsorption of thecontaminate the nanoparticles can be isolated by applying a magneticfield to the water. The amount of magnetization can depend on thestrength of the magnetic field applied to the water. Those skilled inthe art will understand that any type of magnet can be used forisolating Al-MNPs from the water. For instance, in some exemplaryembodiments the magnet can be a permanent magnet. In other exemplaryembodiments, the magnet can be an electromagnet.

One benefit of the present invention is the ability to easily regeneratethe plurality of Al-MNPs from the contaminate-adsorbed nanoparticlesafter they are removed from the wastewater. In some exemplaryembodiments regenerating the plurality of nanoparticles can comprisecontacting the contaminate-adsorbed nanoparticles with a regenerationagent. In some exemplary embodiments the regeneration agent can bealuminum sulfate. The regeneration agent can react with thecontaminate-adsorbed Al-MNPs wherein the regeneration agent selectivelyand/or competitively couples to the contaminate to form acontaminate-coupled regeneration agent and a contaminate-free Al-MNPthus regenerating the Al-MNP. The contaminate-coupled regeneration agentcan then precipitate out of solution for use in other processes, such asfertilizers, and the like.

Another embodiment of the present invention can comprise analuminum-phosphate magnetic nanoparticle produced by the processcomprising: contacting an aluminum-doped magnetic nanoparticle with aphosphate mixture the exposing facilitating adsorption of the phosphateto a surface of the aluminum-doped magnetic nanoparticle; and isolatingthe aluminum-phosphate nanoparticles by applying a magnetic field to themixture. The process for producing the aluminum-phosphate magneticnanoparticle can include some or all of the features described above.

EXAMPLES Example 1

Methods

Chemicals and Materials

Materials:

Ammonium hydroxide (NH₃OH), ferrous chloride (FeCl₂), ferric chloride(FeCl₃), hydrochloric acid (HCl), nitric acid (HNO₃), aluminum sulfate(Al₂(SO₄)₃), monopotassium phosphate (KH₂PO₄), sodium chloride (NaCl),sodium nitrate (NaNO₃), sodium sulfate (Na₂SO₄), and sodium hydroxide(NaOH) were obtained from Sigma Aldrich (St Louis, Mo., USA) and used asreceived. ICP standards for Fe, Al, and P were purchased fromHigh-Purity Standards (Charleston, S.C., USA). Poultry rinsingwastewater was obtained by rinsing a whole bird carcass, purchased at alocal grocery store, in 400 ml of DI water. Wastewater samples afterprimary and secondary treatment were collected from local municipalwastewater treatment plants.

Synthesis and Characterization

Preparation of aluminum-doped magnetic nanoparticles: A diluted NH₃OHsolution at pH 12 was purged with argon and heated to 90° C. for onehour. Then, a stoichiometric mixture of FeCl₂/FeCl₃/Al₂(SO₄)₃ was addeddropwise into the ammonium solution. The mixture was refluxed for twohours with argon purging. The system was then cooled to roomtemperature, and the black precipitates at the bottom of flask werecollected with a magnet (DynaMag-50, Life Technology) and washed threetimes with DI water. The final product was re-suspended in DI water forstorage.

Material characterization: X-ray diffraction (XRD) data was collectedwith a Bruker D8 Advanced X-Ray Diffractometer with a copper Kα sourceover a 15-85° 2θ range. Magnetic measurements were performed using aQuantum Design MPMS-5S SQUID magnetometer. Particles were immobilized inicosane (C₂₀H₄₂, Aldrich) for hysteresis measurements. High resolutionscanning transmission electron microcopy imaging and elemental mappingwere conducted on Hitachi HD-2700 with Oxford XMax EDX detector.Scanning electron microscopy (SEM) imaging and elemental mapping wereperformed on Hitachi 8230 equipped with Oxford XMax EDX detector. Thecomposition of the Al-MNP was also determined by inductively coupledplasma-optical emission spectrometry (ICP-OES). For this procedure, aknown amount of nanoparticles was digested by concentrated HNO₃ in aParr bomb at 200° C. for two hours. Serial dilutions were performed in2% HNO₃. Elemental analysis for Fe, Al, and P was performed on PerkinElmer Optima 8000 ICP-OES. P levels in water samples were also measuredby ICP-OES.

Synchrotron X-ray Absorption Spectroscopy (XAS) Analysis:Synchrotron-based X-ray absorption near edge structure (XANES) analysiswas conducted at P K-edges to investigate the local coordinationenvironment of P during phosphate sorption onto the pure and Al-dopedMNP. XANES spectra were also collected on two reference compounds AlPO₄(VWR) and FePO₄ (Aldrich). Phosphate sorption samples were obtained byreacting 3 mg of pure or Al-MNP with 30 mL of 30 ppm phosphate solutionunder constant shaking conditions for two hours. At the end of reaction,an external magnet was used to separate the adsorbent from the liquidphase, followed by DI rinse (three times). The wet pastes were stored at−20° C. and only thawed before XAS data collection. Data collection wasconducted in fluorescence mode at beamline 14-3 at the StanfordSynchrotron Radiation Light source (SSRL), Menlo Park, Calif. Referencesamples were grounded into fine powders and brushed evenly onto P-freeKapton tapes. Excess powders were blown off to achieve a homogeneousthin film. For phosphate sorption samples, a thin layer of the thawedwet paste were directly mounted onto Kapton tapes and covered by a layerof 3 mm polypropylene film to avoid evaporation. The sample-loaded tapeswere then mounted to a sample holder. The sample chamber was maintainedunder a He atmosphere at room temperature, and the spectra werecollected in fluorescence mode using a PIPS detector. Energy calibrationused AlPO₄ by setting the edge position (peak maxima of the firstderivative) to be 2152.8 eV. Spectra for this reference sample wereperiodically collected to monitor possible energy shifting, which wasnot observed during data collection. XANES spectra were collected atenergy ranges from 2100 to 2485 eV. Multiple scans were collected foreach sample averaged, and normalized for further analysis. Data analysiswas performed using the software SIXPack and Ifeffit.

Phosphate Adsorption Experiments

Adsorption Isothermal experiment: A phosphate stock solution with aconcentration of 1000 ppm was prepared by dissolving KH₂PO₄ in DI water.A volume of 30 mL of phosphate with concentrations ranging from 1 to 40ppm was prepared in DI water in a 50 mL centrifuge tube. Then, 5 mL ofthe solution were taken out as a positive control for P levelmeasurement. 3 and 6 mg of Al-MNP, respectively, were added into thephosphate solutions and shaken on a wrist shaker overnight. Then, anexternal magnet was used to separate the adsorbent from the liquidphase. The supernatant was collected and the concentration of P insupernatant was measured by ICP-OES. The adsorption capacity ofphosphate by Al-MNP can be expressed as follows:

$\begin{matrix}{q_{e} = {( {C_{0} - C_{e}} )\frac{V}{m}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where q_(e) is the adsorption capacity at equilibrium (mg/g), C₀ isinitial concentration of solution (mg/L), C_(e) is the concentration atthe adsorption equilibrium (mg/L), V is the volume of water sample (L),and m is the mass of the sorbent (g). Both Langmuir and Freundlichmodels were tested for fitting the sorption isotherms. The Langmuirequation is expressed as:

$\begin{matrix}{\frac{C_{e}}{q_{e}} = {{\frac{1}{q_{m}}C_{e}} + \frac{1}{K_{L}q_{m}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

where q_(m) is the maximum adsorption capacity (mg/g), and K_(L) is theLangmuir adsorption constant (L/mg). If the adsorption system followed aLangmuir adsorption model, then a plot of C_(e)/q_(e) versus C_(e) wouldproduce a straight line from which the constants q_(m) and K_(L) couldbe evaluated.

The Freundlich adsorption isotherm is represented by the followingequation:

$\begin{matrix}{{\ln\; q_{e}} = {{\ln\; K_{F}} + {\frac{1}{n}\ln\; C_{e}}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where K_(F) is a Freundlich constant in (mg/g)(L/mg)^(1/n), and n is aFreundlich constant representing the adsorption intensity. If theadsorption system followed the Freundlich model, then a plot of lnq_(e)versus lnC_(e) would give a straight line from which constants K_(F) andn could be evaluated.

Phosphate removal studies: Phosphate removal experiments were performedin 10 mL of 10 ppm phosphate solutions with 0.1 M NaNO₃ as backgroundelectrolyte. 3 mg of Al-MNP was added into the phosphate solution andmixed for 30 minutes using a wrist shaker. Then, a magnet was used toattract the particles to the side of the tube, and the supernatant wascollected for ICP analysis. For experiments involving variable pH, thepH values were adjusted by adding diluted HNO₃ or NaOH. Phosphateremoval efficiency at time t was calculated as:

$\begin{matrix}{{\%\mspace{14mu}{removal}} = {\frac{C_{0} - C_{t}}{C_{0}} \times 100\%}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Dopant LeachingTtest

To determine whether metals from the nanoparticles were leached backinto solution, 3 mg of Al-MNP was added into 10 mL of 10 ppm phosphatesolution and the suspension was shaken for 30 min using a wrist shaker.The supernatant was collected after magnetic separation and analyzed forAl and Fe concentrations by ICP-OES.

Al-MNP Nanoparticle Regeneration

After conducting the Al-MNP in a typical phosphate removal experiment,phosphate-loaded Al-MNPs were soaked in 0.05 M Al₂(SO₄)₃ for fiveminutes. The supernatant and regenerated Al-MNPs were magneticallyseparated, followed by two times of rinsing with 0.1 M NaNO₃.

Results and Discussion

Characterization of Pure and Al-MNPs

The X-ray diffraction patterns of both pure and Al-doped magnetite(Fe₃O₄) magnetic nanoparticles are shown in FIG. 2 . The peaks centeredat 2θ=31°, 36°, 44°, 58° and 63° can be indexed as the (220), (311),(400), (511) and (440) planes of magnetite, in agreement with thestandard magnetite JCPDS card (card no. 19-0629). However, slight peakshifts were observed for Al-MNP. Rietveld refinement was performed toextract the lattice constant and averaged crystallite size, and theresults indicated that the lattice constant was reduced from 8.358 Å inpure MNP to 8.334 Å in Al-MNP and the grain size was also reduced from14.24 nm in pure MNP to 9.88 nm in Al-MNP. The size of the preparedAl-MNP was confirmed to be around 10 nm, as shown in the SEM picture inFIG. 3 .

Synthesis of magnetite in the presence of Al was previously reported toproduce Fe₃O₄—FeAl₂O₄ solid solution. The lattice constant of the dopedFe₃O₄—FeAl₂O₄ solid solution as a function of FeAl₂O₄ concentration X(mol %) at room temperature was described by the following Vegard'sequation:L _(d)(Å)=8.391−0.00190X−0.5X ²×10⁻⁵  Equation 5

The 8.334 Å lattice constant of the Al-MNP corresponded to 30% ofFeAl₂O₄ in the solid solution. SEM-EDX and ICP-OES determined Al:Feratios were 0.30 and 0.31, respectively, corresponding to 34% of FeAl₂O₄in the solid solution. The less amount of FeAl₂O₄ as determined by XRDmight suggest that small amounts of Al ions remained as amorphous Al(oxy)hydroxide phase(s) in the doped nanoparticles. High resolutiontransmission electron microscopy (HRTEM) with energy dispersivespectroscopy (EDX) was employed to examine Al distribution in theobtained Al-MNP nanoparticles. As shown in FIG. 4 , Al exhibited auniform distribution as that of Fe, suggesting structural incorporation.The lattice fringe spacing between two adjacent crystal planes of thenanoparticle was 0.485 nm in the HRTEM image, corresponding to the (111)lattice plane of a single-phase Fe₃O₄.

The magnetic moments of both pure and Al-MNP were measured and comparedas a function of applied magnetic field at a constant temperature of 300K (FIG. 5 ). Both types of nanoparticles show superparamagnetism withouthysteresis and remnant magnetization at room temperature. The saturationmagnetization was found to be 77 emu/g for pure MNP and 26.3 emu/g forAl-MNP. The reduced magnetization for Al-MNP could be explained by thereplacement of Fe³⁺ by nonmagnetic Al³⁺ in octahedral sites in aface-centered cubic lattice structure.

Adsorption Kinetic Studies

To determine phosphate sorption kinetics, 3 mg of Al-MNP was mixed with10 mL of phosphate at concentrations of 10, 20, and 30 ppm (typicalmunicipal wastewater contains 10 to 30 ppm phosphate), and phosphateuptake was measured at various time points (FIG. 6 ). The initialadsorption was fast, with ˜75% of phosphate removed within the first 30min, and greater than 90% of phosphate removal can be achieved in twohours. The fast removal rate can be contributed to the high surface areaof the MNP and the ease of dispersion into the liquid stream for bettermixing with contaminants. Three well-known kinetic models, including thepseudo first order model, pseudo second order models, and theintraparticle diffusion model, were used to fit of the phosphate removalkinetic data. The pseudo first order model was given as:ln(q _(e) −q _(t))=lnq _(e) −k ₁ t  Equation 6

The pseudo second order kinetic model was given as:

$\begin{matrix}{\frac{t}{q_{t}} = {\frac{1}{k_{2}q_{e\;}^{2}} + {\frac{1}{q_{e}}t}}} & {{Equation}\mspace{14mu} 7}\end{matrix}$

The intraparticle diffusion kinetic model is given as:q _(t) =k _(d) t ^(1/2) +C  Equation 8

where q_(t) is the amount of phosphate removed at time t (mg/g), q_(e)is the adsorption capacity at equilibrium (mg/g), k₁ is the pseudo firstorder rate constant (min⁻¹), k₂ is the pseudo second order rate constant(g/(mg·min)), k_(d) is the intraparticle diffusion rate constant(mg/(g·min^(0.5))), and t is the contact time (min). Plots oflog(q_(e)−q_(t)) versus t, t/q_(t) versus t, and q_(t) versus t^(0.5)generated the rate constants, q_(e) and the correlation coefficients R²,which were compared in

TABLE 1 Kinetic parameters for the adsorption of phosphates onto Al-MNPInitial phosphate concentrations (mg/L) 10 20 30 Experimental q_(e)(mg/g) 31.7 43.5 47.1 Pseudo first- k₁ (min⁻¹) 0.015 0.007 0.018 ordermodel q_(e) (mg/g) 12.52 10.59 9.49 R² 0.972 0.93 0.94 Pseudo second- k₂(g/(mg · min)) 0.177 0.0027 0.0065 order mode q_(e) (mg/g) 30.3 43.8647.62 R² 0.992 0.999 0.999 Intra-particle k_(d) (mg/(g · min^(0.5)))1.067 33.21 39.65 diffusion model R² 0.992 0.91 0.498

The most likely kinetic model for the adsorption of phosphate on Al-MNPwas the pseudo second order model. Although the correlation coefficientfor pseudo first order was greater than 0.9, there was a largedifference between the experimental and theoretical adsorbed masses atequilibrium. This result indicated that the adsorption of phosphatesonto Al-MNP was not an ideal pseudo first order reaction. Theintraparticle diffusion model describes the adsorption processes wherethe rate of adsorption depends on the speed at which the adsorbatediffuses towards adsorbent. A better fit was obtained using this modelat a low phosphate concentration, indicating some degree ofdiffusion-controlled step involved during the phosphate removal processat low phosphate levels. However, at higher phosphate concentrations,the rate limiting step became surface adsorption.

For the pseudo second order model, the correlation coefficients for allinitial phosphate concentrations were higher than 0.99. In addition, thedifference between the experimental and theoretical adsorbed masses atequilibrium was very small (less than 1%), indicating that theadsorption of phosphate on Al-MNP could be a pseudo second orderreaction. In this model, the rate limiting step was the surfaceadsorption that involved chemisorption, where the phosphate removal froma solution was due to physicochemical interactions between the twophases. The pseudo second order model of phosphate removal was plottedas a function of time in FIG. 7 .

pH Effects

The effect of pH on phosphate removal was also examined (FIG. 8 ). Theseresults showed that the removal efficiency was independent of the pH forpH 4 to 9. At pH 10, phosphate removal efficiency dropped from 95% toabout 59%, likely due to the leaching of doped Al ions from Al-MNP asdetermined by ICP-OES analysis of the solution.

Adsorption Interference Studies

The potential influence of other common constituents in wastewaters on Premoval by Al-MNP was also tested. Phosphate removal was assessed in thepresence of 10 mg/L chloride (Cl⁻), nitrate (NO₃ ⁻), and sulfate (SO₄²⁻). The effects of these coexisting anions on phosphate removal areshown in FIG. 9 . Results showed that the presence of these anions onlyslightly reduced phosphate adsorption by 5 to 7%, suggesting that theAl-MNP was selective to phosphate adsorption. Poultry rinse water, whichcontained high level of organic matters, fat, and proteins, was alsotested for phosphate removal. The phosphate level in the rinsing waterwas around 30 mg/L. The rinse water was filtered through a 1 μm syringefilter to prevent clogging during ICP measurements, and then diluted tohave a final phosphate level of 10 ppm for direct comparison to theother experiments. The data can also be found in FIG. 9 . All of thetests performed indicated that the presence of additional anions, aswell as organic materials from poultry rinse, did not interfere with thephosphate removal efficacy.

Adsorption Isotherm Studies

The sorption isotherm was examined to understand how phosphate anionsdistribute themselves between liquid and solid phases at equilibrium.The most common adsorption models are the Langmuir model (correspondingto a monolayer of homogeneous adsorbent surface) and the Freundlichmodel (corresponding to a heterogeneous adsorbent surface). Table 2summarized the parameters obtained from the curve fitting with twomodels. Clearly, the experimental data fit better with the Langmuirmodel of a monolayer homogeneous adsorbent surface, and the maximumadsorption capacity was greater than 100 mg/g. These results surpassedthe commercially available adsorbents as mentioned in the literature andthe reported magnetic adsorbents for phosphate, as shown in Table 3.

TABLE 2 Adsorption isotherm parameters with Langmuir and Freundlichmodels Freundlich model Langmuir model K_(F) Amount of q_(m) K_(L)(mg/g) adsorbent (mg/g) (L/mg) R_(L) R² (L/mg)^(1/n) n R² 3 mg Al-MNP102.15 1.09 0.022 0.988 43.82 2.88 0.806 6 mg Al-MNP 81.31 1.09 0.0220.996 32.07 2.57 0.444

TABLE 3 Comparison of adsorption capacity of Al-MNP with other magneticadsorbents Maximum Adsorption Adsorbent Capacity (mg PO₄/g) Diatomfrustules coated on Fe₃O₄ 4.89 Core-shell Fe₃O₄ @LDHs composite26.5-36.9 Magnetic iron oxide nanoparticles 5.03 Fe—Zr binary oxide13.65 Tetraethylenepentamine-coated Fe₃O₄  81-102 Magnetite modifiedwith aluminum/silica 25.64 Polyacrylamide coated Fe₃O₄ 28.95 ZrO₂ shelland magnetite core 39.1 (Fe₃O₄@mZrO₂) Mesoporous rodlike NiFe₂O₄ 39.3Al—Fe₃O₄ 102.15

The increased adsorption capacity originated from the doped Al. The pureMNP had a much lower capacity for phosphate adsorption compared toAl-MNP. In addition, the treated Al-MNP at a higher pH lost itsphosphate binding capability as a results of the loss of Al from thedoped particle.

The Langmuir constant K_(L) is related to the standard free energy ofadsorption (ΔG°) and indicates the phosphate binding affinity of theadsorbent. A high K_(L) value indicates greater affinity for phosphateadsorption by an adsorbent. To determine whether the adsorption isfavorable, the essential characteristics of the Langmuir equation can beexpressed in a dimensionless separation factor or equilibrium parameter,R_(L), as defined in Equation 8, where C₀ is the highest initialphosphate concentration (mg/L). The factor R_(L) was within the range of0 and 1.0, suggesting the favorability of phosphate adsorption onto theAl-MNP. In addition, the calculated n value in the Freundlich model wasgreater than 1, indicating a favorable adsorption.

$\begin{matrix}{R_{L} = \frac{1}{1 + {K_{L}C_{0}}}} & {{Equation}\mspace{14mu} 9}\end{matrix}$

Phosphate Uptake Mechanism

P K-edge XANES analysis was conducted to elucidate the mechanism(s) forthe enhanced phosphate uptake on Al-MNPs as compared to pure MNPs. TheXANES spectra of P sorbed MNP and FePO₄ both exhibit a unique pre-edgefeature at ˜2150 eV (dashed line in FIG. 10 ). The presence of thispre-edge peak has been previously observed for phosphate mineralscontaining Fe(III) species, such as heterosite and strengite. As acomparison, Al-containing phosphate minerals, such as AlPO₄ in thedescribed system, does not have such pre-edge peak. Therefore, in asimple controlled system such as the described system, the presence andamplitude of this pre-edge peak can be used to identify the relativecontribution of P—Fe association. Previous studies have demonstrated theformation of inner-sphere complexes (e.g. bond formation betweenphosphate tetrahedra and surface Fe atoms) during the sorption ofphosphate onto Fe and Al oxide minerals. The intensity of the pre-edgefeature can be correlated with the relative proportion of phosphatebonded with Al(III) versus Fe(III). Therefore, the much lower intensityof this pre-edge feature in the P sorbed Al-MNP sample suggests thatlarge amount of phosphate was bonded to surface Al sites versus Fesites.

Metal Leaching and Particle Regeneration

Doped Al was securely incorporated into the magnetite structure. Regularrinsing did not remove Al from the doped magnetic nanoparticles. Thisobservation was confirmed by examining the metal levels in the liquidphase after phosphate removal. In a typical phosphate removalexperiment, after one minute magnetic separation of the particles fromthe liquid phase, the supernatant only contained 15 ppb Al and 30 ppbFe, meaning 99.94% of magnetic particles were separated from the liquidphase. The remaining Al and Fe in the treated water originated from theresidual magnetic nanoparticles in the liquid phase.

To lower the operation cost, the regeneration of Al-MNP was explored. Itwas discovered that phosphate adsorbed onto the Al-MNP can easily bestripped off through a competitive binding between the Al on the Al-MNPand Al in the solution. Using a 0.05M Al³⁺ solution, the adsorbedphosphate was removed from the Al-MNP. The regenerated Al-MNP were thenrinsed twice with 0.1 M NaNO₃ to remove any loosely attached Al on theparticle before being used again for phosphate removal. FIG. 11 showsthe regeneration capability of Al-MNP. It was clear that regeneratedAl-MNP did not lose much phosphate binding capability after 11 cycles ofregeneration.

Wastewater Treatment

The Al-MNPs were tested for phosphate removal on tap water, primarywastewater effluent, and secondary wastewater effluent. Without anyadditional pretreatment, these waters were directly treated with Al-MNPto examine the matrix effect on the phosphate removal efficacy. Table 4summarizes the phosphate levels before and after the treatment. Due tothe high phosphate concentration in the sample collected from primaryeffluent, 10 mg of Al-MNP was used; 3 mg was used for both tap water andsecondary effluent water. Great phosphate reductions (above 80%) wereobtained in all three water samples within 30 minutes. Although thephosphate level in the treated primary effluent sample was still high (2ppm), either adding more adsorbents or performing a secondary Al-MNPtreatment would reduce the phosphate level in the primary effluent tobelow 1 ppm. The phosphate level in tap water was greater than thesecondary effluent because blended phosphates (1 to 5 ppm) are typicallyadded to the drinking water as a corrosion inhibitor to prevent theleaching of lead and copper from pipes and fixtures.

TABLE 4 Phosphate removal in wastewater samples Sample Amount ofPhosphate level Phosphate level Phosphate type adsorbent (mg) before(ppm) after (ppm) removal (%) Tap water 3 1.45 ± 0.02 0.262 ± 0.01   82% Primary 10 26.4 ± 0.35 2.01 ± 0.03 92.3% effluent Secondary 3 0.95± 0.04  0.17 ± 0.002   82% effluent

Conclusion

A simple and low-cost method to remove phosphate from wastewater streamsthrough the use of unique aluminum-doped magnetic nanoparticles weredemonstrated. Aluminum-doped magnetic nanoparticles were synthesizedusing a co-precipitation method. Structure and composition analysis ofthe prepared magnetic nanoparticles indicated an inverse spinalstructure with a composition of FeAl_(0.75)Fe_(1.25)O₄. These particlesnot only have a great adsorption capacity to phosphate. They also havean excellent selectivity for phosphate removal, even in the presence ofother anions and organic materials such as fat and proteins. Thisproperty allows the particles to be used for a variety of wastewatertreatments, as supported by the high levels of removal in poultry rinsewater, tap water, and local municipal wastewater. Used Al-MNP can beregenerated for multiple cycles through a competitive binding chemistryby dispersing the particles in an aluminum sulfate solution. Therefore,the overall costs for phosphate removal are fairly low. Doped magneticnanoparticles can be used as a promising adsorbent for phosphate removalin wastewaters.

Example 2

Methods

Chemicals and Materials

Materials:

Ferrous chloride (FeCl₂), ferric chloride (FeCl₃), hydrochloric acid(HCl), nitric acid (HNO₃), aluminum sulfate (Al₂(SO₄)₃), monopotassiumphosphate (KH₂PO₄), potassium antimonyl tartrate, ammonium molybdate,ascorbic acid, and sodium hydroxide (NaOH) were obtained from SigmaAldrich (St Louis, Mo., USA) and used as received. ICP standards for Fe,Al, and P were purchased from High-Purity Standards (Charleston, S.C.,USA).

MNP Synthesis and Characterization

Preparation of aluminum-doped magnetic nanoparticles: Al-MNP wasprepared by first dissolving stoichiometric amounts of Al₂(SO₄)₃, FeCl₃,and FeCl₂ in 300 ml of deionized water. The solution was heated to 80°C., then 100 ml of 1.5 M NaOH were added and maintained at a temperaturebetween 80-100° C. for ten minutes. A black precipitate was producedupon addition of NaOH. Finally, the cooled black suspension was placedon a magnetic separator (DynaMag-50, Life Technology) and washed fivetimes with DI water. The final Al-MNP suspension was stored in DI waterat room temperature.

Material characterization: X-ray diffraction (XRD) data was collectedwith a Bruker D8 Advanced X-Ray Diffractometer with a copper Kα sourceover a 15-85° 2θ range. Magnetic measurements were performed using aQuantum Design MPMS-5S SQUID magnetometer. Particles were immobilized inicosane (C₂₀H₄₂, Aldrich) for hysteresis measurements. The compositionof the Al-MNP was determined by inductively coupled plasma-opticalemission spectrometry (ICP-OES). For this procedure, a known amount ofnanoparticles was digested by concentrated HNO₃ in a Parr bomb at 200°C. for two hours. Serial dilutions were performed in 2% HNO₃. Elementalanalysis for Fe, Al, and P was performed on Perkin Elmer Optima 8000ICP-OES.

Wastewater Collection

Poultry processing wastewater samples were collected at a local poultryprocessing plant. The wastewater treatment system contains screening toremove the large particulates, dissolved air flotation (DAF) system toremove suspended solids, oil, and grease, an activated sludge system toreduce BOD and COD, a chemical DAF to remove excess TP and anequalization pond. Final effluent of pond is discharged to publicmunicipal system, as shown in FIG. 12 . Wastewater samples werecollected from the effluent of physical screening (raw), effluent of DAF(DAF), effluent of biological treatment (bio), effluent of chemical DAF(chemical DAF) and the final effluent (pond) following the standardwastewater sampling procedures developed by EPA. One gallon of eachwastewater sample was manually collected in acid-cleaned glass bottles,stored at 4° C. and transported to the lab for analysis. Samples wereanalyzed as soon as possible after collection. Portions of samples werepreserved with H₂SO₄ and stored at 4° C. for COD, TKN and FOG tests ifthe analyses cannot be finished in 24 hours.

Wastewater Characterization

Parameters including chemical oxygen demand (COD), total suspendedsolids (TSS), total dissolved solids (TDS), fat-oil-grease (FOG), totalKjeldahl nitrogen (TKN), and total phosphates (TP) were measured forwastewater characterizations. COD was measured using the Hach method8000 wherein 2 ml of wastewater samples were digested with a CODdigestion reagent (Hach, Loveland, Colo., USA) in a Hach DRB200 reactorfor two hours. Then a Hach DR 3900 colorimeter was used to read the CODlevel. TKN was measured using the Hach method 10242 in which inorganicand organic nitrogen are oxidized to nitrate by digestion withperoxodisulfate. The difference of nitrate before and after thedigestion was calculated as TKN. TSS and TDS were measuredgravimetrically by filtering a known volume of wastewater (from 2 to 40ml depending on the level of contamination) and measuring the weight ofthe residue on the filter after thorough drying (TSS). The filtrate wasevaporated, and the remaining residue was weighed (TDS). Hexaneextractable FOG was measured gravimetrically by extracting 350 mL ofwater sample with multiple aliquots of 25 ml hexane followed by theevaporation of all of the solvent. The residue was weighed. Eachmeasurement was duplicated, and the averaged results were reported.

P Speciation

P species in poultry wastewater samples were differentiated using EPA365.2 method. In bodies of water, phosphorus is present in severalsoluble and particulate forms such as organically bound phosphorus, andinorganic orthophosphates. FIG. 13 summarizes the testing methods to beused to characterize these P species in liquid streams. Basically,wastewater samples were split into two portions. One portion wasfiltered through a 0.45 m filter and the second portion was analyzedwithout any filtration. The unfiltered water sample was treated by threemethods independently to obtain total reactive phosphorus (mainlyorthophosphate A), total acid hydrolysable phosphorus (combination oforthophosphate A and polyphosphate B), total phosphorus C(orthophosphate A, polyphosphate B and organo P species D). Similarapproaches were conducted on the filtered water samples to get solublereactive phosphorus (E), total soluble acid hydrolysable phosphorus(combination of soluble orthophosphate E and soluble acid hydrolysablephosphorus F), and total soluble phosphorus G (E, F and organo P speciesH). The differences between C and G, A and E, B and F, and D and Hgenerate the levels of P species in the particulate forms.Alternatively, total phosphorus in the filtered and unfilteredwastewater samples can be measured by ICP-OES method after aciddigestion.

Ascorbic Acid Colorimetric Method

4 mM potassium antimonyl tartrate solution, 0.03 M ammonium molybdateand 0.1 M ascorbic acid were prepared in DI waster. A combined reagentmixture was created by mixing 50 ml of 5 N sulfuric acid, 5 ml potassiumantimonyl tartrate solution, 15 ml ammonium molybdate solution, and 30ml ascorbic acid solution in order at room temperature. Next, 1.6 ml ofthe reagent mix were added to 10 ml of each sample. After ten minutes,each sample had its absorbance measured at 880 nm by UV-vis.

Acid Hydrolysis for Total Acid Hydrolysable Phosphorus Analysis

An acid mixture containing 5.4M H₂SO₄ and 0.06M HNO₃ solution wasprepared in DI water. 100 μl of the acid solution were added to 10 ml ofeach of the wastewater samples. The samples were then placed in anautoclave for 30 minutes at 121° C. The samples were allowed to cool toroom temperature, and had the ascorbic acid test performed on eachsample, then had the absorbencies measured by UV-vis.

Acid Digestion for Total Phosphorus Analysis

200 μl of 5.4M sulfuric acid and 80 mg of ammonia persulfate were addedto 10 ml of each wastewater sample. The samples were then placed in anautoclave for 30 minutes at 121° C. The samples were allowed to cool toroom temperature and had the ascorbic acid test performed on eachsample, then had the absorbencies measured by UV-vis.

Phosphate Adsorption Experiment

Phosphate removal studies: Each wastewater sample had its totalphosphorus concentration measured by ICP. The mass ratio of Al-MNP to TPin 50:1 was used for wastewater treatment. Al-MNPs were added to 50 mlcentrifuge tubes containing 40 ml of each wastewater sample and thetubes were placed on a wrist-action shaker for about one hour, thenplaced in a magnetic separator. The supernatants were drawn from thetubes after ten minutes on the separator, then had their new phosphorusconcentrations measured by ICP. Phosphorus removal efficiency at time twas calculated as:

$\begin{matrix}{{\%\mspace{14mu}{removal}} = {\frac{C_{0} - C_{t}}{C_{0}} \times 100\%}} & {{Equation}\mspace{14mu} 10}\end{matrix}$

where C_(o) and C_(t) are the concentrations of P before and after onehour of the Al-MNP treatment.

Results and Discussion

Nanomaterial Characterization

Prepared magnetic materials were characterized using XRD, SEM andmagnetometer to measure the crystalline structure, particle size andmagnetic properties, respectively. The locations and intensities ofpeaks in the X-ray diffraction pattern (FIG. 14 ) of the Al-MNP are inagreement with the standard magnetite (red lines) JCPDS card (card no.19-0629), indicating a magnetite structure with aluminum fullyincorporated in the cubic inverse spinel lattice. The formation of solidsolution Fe₃O₄—FeAl₂O₄ was confirmed previously and the lattice constantof the doped Fe₃O₄—FeAl₂O₄ solid solution was reduced, compared to thepure Fe₃O₄. The averaged crystallite size was estimated using XRD, andthe results indicated that the averaged grain size was about 9.9 nm inAl-MNP.

The saturation magnetization of the prepared Al-MNP displayedsuperparamagnetism without hysteresis and remnant magnetization at roomtemperature. The saturation magnetizations of Al-MNP are negativecorrelated with the doping level of Al. They are 77, 46, 34 and 18 emu/gfor 0%, 10%, 15% and 20% of Al doping respectively as shown in FIG. 15 .The linear reduced magnetization for Al-MNP could be explained by thereplacement of Fe³⁺ by nonmagnetic Al³⁺ in octahedral sites in aface-centered cubic lattice structure. Al-MNP with 20% of Al doping wasused in this study due to the higher adsorption capacity toward Pspecies.

Wastewater Characterization

The treatment methods for poultry processing wastewater vary greatlydepending on the discharge methods; either by indirect discharge (thetreated wastewater is sent to a publicly owned treatment plant) or bydirect discharge (treated wastewater is discharged into a stream orother receiving water body). Almost 94% of poultry processing plants areindirect dischargers. Wastewater samples were collected from a poultryprocessing plant where the wastewater is indirectly discharged. Theplant processes about 200,000 birds/day with average wastewater flow of1.7 million gallon per day. A series of wastewater treatment stepsincluding DAF systems and aerobic system, as shown in FIG. 12 , arefollowed to reduce the contamination levels. Polymer based coagulantsare added in the DAF system to assist the removal of suspendedparticles. The effluent of DAF is then transferred to a completelymixed, activated sludge tank designed to address soluble COD and BOD.The effluent from the biological treatment is further treated inchemical DAF, where ferric salt and polymers are added to reduce TP. Theeffluent from chemical DAF and the stormwater runoffs are sent to anequalization pond before they are discharged to a publicly ownedTreatment Works (POTW).

Changes in contamination levels were monitored by collecting wastewatersamples after each step of the treatment process. Parameters includingpH, COD, TSS, TDS, FOG, TKN, and TP were characterized. The results arelisted in Table 5 below. The post screening effluent (Raw) contains highlevels of COD, TSS, FOG, TKN and TP. The level of contaminants in Raware in good agreements with the reported literature values. After thechemically enhanced DAF treatment, more than 98% of TSS and 90% of FOGwere removed. Moderate removals of other contaminants were achievedincluding reductions of COD by 67%, TKN by 52%, and TP by 36%. Theseremoved contaminants were likely associated with the suspended solids.It has been reported that 40% to 50% of COD in screened (1 mm mesh)effluent of meat processing wastewater was in coarse suspended form.This varies considerably from domestic wastewater, in which the COD ispresent mainly in the soluble and colloidal forms.

TABLE 5 Wastewater characterization before and after MNP treatment CODFOG TSS TDS Total N (ppm) Type pH (ppm) (ppm) (ppm) (ppm) NO₃ + NO₂ TKNTP (ppm) Raw 5.4 3495 ± 49  517 ± 21  1195 ± 21  865 ± 64  6.59 ± 1.33 140 ± 9.89 51.2 ± 3.89 Treated  439 ± 0.71 3 ± 2 41 ± 14 670 ± 14  4.52± 2.43 62.6 ± 13.5   3 ± 0.07 Reduction % 87.4 99.4 96.6 22.5 31.4 55.394.1 DAF 5.1  715 ± 7  18 ± 12 17 ± 5  852 ± 24  3.62 ± 0.32 66.8 ± 1.4839.58 ± 0.32  Treated  401 ± 4.24 4 ± 3 36 ± 18 680 ± 12  4.46 ± 0.9757.6 ± 9.05 1.66 ± 0.06 Reduction % 43.9 77.8 −118 20.2 NA 13.8 95.8Biological 6.8 1160 ± 71  107 ± 10  600 ± 0  625 ± 0  3.14 ± 0.62 110.3± 15.13 55.77 ± 1.48  Treated  192 ± 0.71 18 ± 10 148 ± 68  658 ± 3 2.95 ± 0.73 66.5 ± 3.61  2.86 ± 0.006 Reduction % 83.4 83.2 75.3 NA 6.0539.5 94.9 Chemical DAF 6.5 226 ± 4  BD 70 ± 38 657 ± 9  1.96 ± 0.0988.85 ± 29.9   4.7 ± 0.19 Treated  187 ± 2.12 NA 36 ± 18 698 ± 6  2.58 ±0.41 72.2 ± 4.81 0.59 ± 0.03 Reduction % 17.3 NA 48.6 NA NA 18.4 87.4Pond 6.7 111 ± 4  BD 127 ± 47  623 ± 5  2.23 ± 1.69 88.25 ± 0.78  12.18± 0.41  Treated 77.5 ± 3.53 NA 48 ± 4  641 ± 14  2.84 ± 0.19 73.6 ± 0.781.19 ± 0.03 Reduction % 30.2 NA 62.2 NA NA 16.6 90.2

Dissolved air flotation (DAF) is applied widely in the pretreatment ofindustrial wastewater. Air in the DAF system is usually dissolved inwater under pressure (400-600 kPa) in a saturator and microbubbles arereleased through nozzles or special valves at the bottom entrance to thecontact zone. In the contact zone, microbubbles attach to flocs toproduce bubble-floc aggregates. Then the bubble-floc aggregates areseparated from water due to the density difference in the separationzone. Flocculants and/or coagulants may be added in the removal oftargeted contaminants such as solids/fats to enhance the performance ofDAF. Typical reductions of COD, TSS and FOG are in the range of 50% to80% depending on the air pressure and the type of flocculants inside theDAF. DAF has also been used to remove TP in the meat processingwastewater.

The DAF effluent was delivered to an activated sludge treatment systemto remove organic matters. However, it only reduced COD by 13%. Inaddition, the amount of TSS increased from 17 ppm to 600 ppm, FOG from18 ppm to 107 ppm, TKN increased from 66.8 ppm to 110 ppm, and TPincreased from 18.6 ppm to 50.6 ppm. These increases could be attributedto the presence of unsettled sludge in the effluent.

Activated sludge system is used to reduce BOD and COD, and to convertammonia to nitrate. The typical removal rate for COD, TP, TKN are in therange of 80 to 90%. However, we only observed a 13% reduction of CODwhile levels of TP, suspended solids and TKN were increased, indicatingthe biological treatment was not working properly. The performance ofthe aerated biological treatment is dependent on the many factorsincluding hydraulic retention time, the age and health of the sludge. Asludge age of 5-20 days is recommended for treating slaughterhousewastewater as proteins are less readily biodegradable than simplemolecules. In addition, one limitation of this technology is the poorsettling floc in activated sludge systems while treating slaughterhousewastewater. This was due to a combination of the high fat content of theinfluent and a low DO concentration in the activated sludge reactor. Theincreased TSS, TP and TKN in the effluent are likely remnants from theunsettled floc.

The effluent of activated sludge was sent to another DAF system toremove TP, where the level of TP was reduced TP from 50.6 ppm to 4.14ppm with additional removals of COD and TSS. The level of FOG was belowthe detection limit after this step of treatment. The effluent ofchemical DAF was sent to an equalization pond where the stormwaterrunoffs were also collected. The final effluent was then discharged toPOTW. It's interesting to note, compared to the effluent of chemicalDAF, that the level of COD was 50% reduced in the final effluent ofequalization pond while the levels of TSS, TKN and TP were allincreased. The level of TDS remains relative unchanged along thetreatment process. It's speculated that the increased TSS, TKN and TPwere from inorganic sources in the equalization pond or stormwaterrunoffs in the processing facility.

Chemical based P removal processes convert the soluble P species intothe particulate forms which are then separated from the liquid using DAFtreatment (chemical DAF). Chemical DAF was typically applied after thebiological treatment as the effluent of biological treatment has betterquality and is more stable. The local poultry processing plant uses bothferric salts and cationic polymers in chemical DAF to remove TP. It wasobserved that above 90% of TP was removed in the chemical DAF, which wasin good agreement with the reported performance.

P Speciation in Poultry Wastewater

For phosphorus, most permit limits are based on TP so all forms of P inthe final effluent need to be considered for P reduction. The forms of Pare classified based on their solubility (pass 0.45 μm filter) andreactivity in acid. Both particulate and soluble form of phosphorus canbe fractionized into reactive phosphorus (normally assumed as ortho-P),acid hydrolysable phosphorus (e.g. polyphosphate and condensed P), andorganic phosphorus (e.g. intracellular molecules that containphosphorus).

P speciation analyses on wastewater samples collected at differenttreatment stages were conducted to understand the effects of eachtreatment stage on the distribution and variation of P species. As FIGS.16 and 17 show, the TP in the raw influent is composed of 35% sRP, 19%sAHP, 20% sOP, 16% pRP and 10% pOP. A study indicated that the TP inmunicipal effluent from primary clarifiers contains roughly 60% solublereactive phosphate (sRP), 17% particulate reactive phosphate (pRP), 20%acid hydrolysable phosphorus in the particulate form (pAHP), 3% oforganic phosphorus in both soluble and particulate forms. And thewastewater from the dairy processing industry contained 23.14% sRP,15.3% sAHP, 50.9% sOP, 8.5% pRP, 1% of pAHP and 1.2% pOP of the TP.Compared to the composition of P species in the effluent of a primaryclarifier in a sewage treatment plant, the percentages of sRP and sAHPin food processing wastewater are lower while the percentages of sOP andpOP are higher. Acid hydrolysable phosphorus are mainly condensedphosphate and they are used in water treatment to prevent scaleformation and corrosion control.

After the first DAF treatment, all the P species in particulate formswere reduced significantly while the soluble P species remained atsimilar levels. Aerobic biological treatment reduced some soluble formsof P (29.6% reduction of sRP and 20% reduction of sOP), which is lowcompared to a step-feed biological nutrient removal system where over95% of sRP was removed. In addition, total particulate phosphorus (TPP)was increased dramatically due to the unsettled sludge in the effluent.The distribution of P species can be found in Table 6 below. Almost halfof TP were from TPP.

TABLE 6 P Speciation in wastewater before and after the MNP treatment TPTsP sRP sAHP sOP TpP pRP pAHP pOP RAW 51.2 37.55 17.9 9.59 10.06 13.658.4 0 5.25 Treated 3 1.28 0 1.28 0 1.72 0.11 1.16 0.45 Reduction % 94.1496.59 100 86.65 100 87.39 98.69 0 91.42 DAF 39.58 37.34 16.53 9.78 11.032.24 0.43 0.48 1.33 Treated 1.66 1.08 0 1.08 0 0.58 0 0.55 0.03Reduction % 95.80 97.10 100 88.95 100 74.10 100 0 97.74 Bio 55.77 29.811.64 9.32 8.84 25.97 11.11 4.45 10.41 Treated 2.86 1.2 0 1.2 0 1.660.25 1.01 0.4 Reduction % 94.87 95.97 100 87.12 100 93.60 97.74 77.3096.15 Chemical DAF 4.7 1.89 0 1.21 0.68 2.81 1.63 0.08 1.1 Treated 0.590.38 0 0.38 0 0.21 0.017 0.19 0 Reduction % 87.44 79.89 NA 68.59 10092.52 98.95 0 100 Pond 12.18 8.54 4.57 2.25 1.72 3.64 2.64 0 1 Treated1.19 0.69 0.41 0.28 0 0.5 0.41 0.09 0 Reduction % 90.22 91.92 91.0287.55 100 86.26 84.46 0 100

Chemical DAF not only removed all the sRP but reduced other P speciesdramatically with combined precipitation and adsorption processes. TPPin the effluent of chemical DAF are about 60% of TP, where pRP is themajor form of TPP (60%) and followed by pOP (˜40%). It has been reportedthat P was predominantly bound to iron in the suspended solids(particulates greater than 0.45 μm) when ferric chloride was used inwastewater treatment. FeCl₃ reacted not only with dissolvedorthophosphate, but also with organic compounds containing P. Theprimary pOP might be orthophosphate monoester and orthophosphate diesterspecies.

The composition of TP in the final effluent consisted of 37.5% sRP,18.5% sAHP, 14% sOP, 21.5% pRP, and 8.5% pOP. The composition of sRP waslow compared to the discharge of a typical sewage treatment plant, wherethe percentage of sRP is in the range of 75% to 90%. The higherpercentage of sRP in the discharge of sewage treatment posed a greaterrisk for similar amounts of total P released to the body of water.

Wastewater Characterization after MNP Treatment

Wastewater parameters were characterized after Al-MNP treatment tounderstand the impacts of the treatment on TP and other pollutants inwastewater. To compare the removal efficiencies of Al-MNP on TP indifferent types of wastewater, the mass ratio of Al-MNP to TP was keptconstant at 50:1 (Al-MNP:TP), which was selected based on the maximumadsorption capacity and contact time. Treated wastewaters werecharacterized to determine the removal efficiencies on the wastewaterparameters the including COD, TSS, TDS, FOG, TKN and TP. The results canbe found in Table 5, above. The removal efficiencies on TP ranged from87.4% in the effluent of chemical DAF to 95.8% in the effluent of DAF.The relative lower removal efficiencies in effluents of chemical DAFcould be caused by the presence of excess ferric chloride in chemicalDAF, which may interfere for the availability of phosphate. About 95% ofTP were removed from the influents of DAF, biological treatment andchemical DAF, indicating high removal efficiency on TP regardless thecompositions of P species.

In addition to TP removal, significant reductions on COD, FOG, and TSSwere also observed in the Al-MNP treated raw wastewater with the removalefficacies of 87.4%, 99.4% and 96.6% respectively. The removalefficacies for TDS, nitrate nitrogen and TKN were moderate with removalefficiencies of 22.5%, 31.4% and 55.3% respectively. For the effluent ofDAF, the removal efficiencies of COD and FOG were 43.9%, and 77.8%respectively. However, the level of TSS increased from 17 ppm to 36 ppm,a 118% increase. This increase in TSS is likely resultant fromexperimental limitations as the amount of TSS present was approachingthe detection limit of the method. It was observed that lower CODreduction was typically obtained for the wastewater samples containedless TSS, indicating that COD associated with TSS were removedefficiently with Al-MNP along with the TSS removal.

Activated carbon is used commonly to reduce COD in wastewater. Powderedactivated carbon and powdered zeolite can only remove 38% and 17% ofCOD, respectively, in landfill leachate after 30 hours of treatment,while in another study, a 30% to 50% of COD reduction in dairywastewater was observed using organo-zeolite. The enhanced adsorptionefficacy was attributed to the organic molecule (stearin-dimethyl-benzylammonium chloride) used for zeolite modification. The same materialcould remove 70% of nitrate nitrogen and 20% of phosphate. About 42% ofCOD and 69% of TSS reduction were obtained using porous concretecontaining iron slag and sand filtration removed 11% of COD and 53% ofTSS in storm runoffs. Granular ferric hydroxide adsorbent yielded a 16%COD removal in the secondary effluents of a municipal wastewatertreatment. Comparing to the reported adsorbents, our Al-MNP removed themajor wastewater contaminants favorably.

P Speciation in Treated Wastewater

P speciation was conducted in the treated wastewaters to examine theremoval preference of Al-MNP on P species. The results can be found inTable 6 above. It was observed that almost all reactive phosphorus(orthophosphate) and organic phosphorus either in soluble or particulateforms were removed preferably over acid hydrolysable phosphorus(polyphosphate), as shown in FIGS. 16 and 17 . The total soluble Presiduals (TsP) in the treated Raw, DAF, bio, chemical DAF and pond wereroughly 43%, 65%, 42%, 65% and 58% of TP respectively while thepercentages of TsP before the treatment were 73.3%, 94.3%, 53.4%, 40.2%and 70.1% respectively. Reduced TsP removal was observed in the effluentof chemical DAF. This may be caused by the presence of ferric chloride,which may interfere with the adsorption of TsP on the active sites ofAl-MNP.

MNP Residue in Treated Water

The contents of iron and aluminum in the treated wastewaters werecompared to those before the Al-MNP treatment to determine the residueof Al-MNP in the treated wastewaters. The results can be found in Table7, below. Negligible amount of Fe and Al can be found in all the treatedwastewater indicating a complete solid/liquid separation under anapplication of an external magnet for ten minutes. In fact, the ironlevels were even reduced in bio, chemical DAF, and pond wastewatersafter Al-MNP treatment.

TABLE 7 Iron and aluminum contents in wastewater Fe (ppm) Al (ppm)Before After Before After Al-MNP Al-MNP Al-MNP Al-MNP Raw 0 ± 0  0.054 ±0.0035 0.003 ± 0     0 ± 0 DAF 0 ± 0 0.22 ± 0.14 0.029 ± 0.018  0.096 ±0.0071 Biological 5.014 ± 0.18   0.24 ± 0.012 0.053 ± 0.011 0.0855 ±0.011  Chemical  1.23 ± 0.015  0.012 ± 0.0035 0 ± 0 0 ± 0 DAF Pond 0.97± 0.07   0.07 ± 0.0057 0 ± 0 0.016 ± 0    Conclusion

Wastewater samples were collected at a local poultry wastewatertreatment plant. They were characterized with high contamination levelsof COD, FOG, TSS and TP. The first DAF system can remove over 98% ofTSS, 90% of FOG, 67% of COD, 52% of TKN and 36% of TP; while over 90% ofTP reduction was achieved in the chemical DAF. P speciation analysis wasperformed on the wastewater collected at the different treatment stagesto monitor the changes and removal of P species. The percentages of TsPvaried from 73%, 94%, 53%, 40% and 70% of TP along the treatment chain.Particularly, the bioavailable sRP varied from 35%, 42%, 21%, 0%, and38% at the different treatment stages. Treatment of Al-MNP on wastewatersamples not only reduced TP significantly (over 90%) in all thewastewater samples but also decreased the levels of other contaminantsincluding COD (20% to 87%), TSS (50% to 97%), and FOG (78% to 99%).Based on these removal efficiencies, the suggested application point ofAl-MNP in the poultry wastewater treatment process will be to treat theeffluent of DAF, where the COD, FOG and TSS have been removedsignificantly. The combination of low cost and ease of application makethe Al-MNP a promising material for wastewater treatment.

It is to be understood that the embodiments and claims disclosed hereinare not limited in their application to the details of construction andarrangement of the components set forth in the description andillustrated in the drawings. Rather, the description and the drawingsprovide examples of the embodiments envisioned. The embodiments andclaims disclosed herein are further capable of other embodiments and ofbeing practiced and carried out in various ways. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purposes of description and should not be regarded as limiting theclaims.

Accordingly, those skilled in the art will appreciate that theconception upon which the application and claims are based can bereadily utilized as a basis for the design of other structures, methods,and systems for carrying out the several purposes of the embodiments andclaims presented in this application. It is important, therefore, thatthe claims be regarded as including such equivalent constructions.

I claim:
 1. A method comprising: dispersing solid solutionaluminum-doped magnetite nanoparticles in a fluid having a contaminate,forming contaminate-adsorbed nanoparticles; applying a magnetic field tothe fluid, which segregates at least a portion of thecontaminate-adsorbed nanoparticles; applying a magnetic field to thefluid, which segregates at least a portion of the contaminate-adsorbednanoparticles; removing at least a portion of the segregatedcontaminate-adsorbed nanoparticles from the fluid; and regenerating withan aluminum solution at least a portion of the removedcontaminate-adsorbed nanoparticles into regenerated solid solutionaluminum-doped magnetite nanoparticles; wherein the solid solutionaluminum-doped magnetite nanoparticles prior to regenerating have aninitial contaminate removal efficacy; and wherein the regenerated solidsolution aluminum-doped magnetite nanoparticles have a regeneratedcontaminate removal efficacy that is at least 70% of the initialcontaminate removal efficacy.
 2. The method of claim 1, wherein thesolid solution aluminum-doped magnetite nanoparticles have a singlecrystal structure.
 3. The method of claim 1, wherein the solid solutionaluminum-doped magnetite nanoparticles are characterized by a maximumcontaminate adsorption capacity of greater than 50 mg/g based on theLangmuir model.
 4. The method of claim 1, wherein the contaminate isselected from the group consisting of biochemical oxygen demand (BOD),chemical oxygen demand (COD), total suspended solids (TSS), totaldissolved solids (TDS), fat-oil-grease (FOG), total Kjeldahl nitrogen(TKN), suspended solids, dissolved solids, and a combination thereof;wherein the solid solution aluminum-doped magnetite nanoparticles aresynthesized from a mixture of ferric salt, ferrous salt, and aluminumsalt with a basic solution including one or both sodium hydroxide andammonium hydroxide; and wherein the solid solution aluminum-dopedmagnetite nanoparticles are characterized by a maximum contaminateadsorption capacity of greater than 50 mg/g based on the Langmuir model.5. The method of claim 1, wherein the solid solution aluminum-dopedmagnetite nanoparticles are synthesized from a mixture of ferric salt,ferrous salt, and aluminum salt with a basic solution including one orboth sodium hydroxide and ammonium hydroxide.
 6. The method of claim 1,wherein an isolation efficiency of the contaminate-adsorbednanoparticles is pH-independent in the range of the fluid pH from 4 to9.
 7. The method of claim 1, wherein the solid solution aluminum-dopedmagnetite nanoparticles are characterized by a maximum contaminateadsorption capacity of greater than 81 mg/g based on the Langmuir model.8. The method of claim 1, wherein the solid solution aluminum-dopedmagnetite nanoparticles are characterized by a maximum contaminateadsorption capacity of greater than 102 mg/g based on the Langmuirmodel.
 9. The method of claim 1, wherein a containment concentration ofthe fluid after removal of at least a portion of the removedcontaminate-adsorbed nanoparticles is from about 40% to about 97% lessthan a containment concentration of the fluid prior to forming thecontaminate-adsorbed nanoparticles.
 10. The method of claim 2, whereinthe solid solution aluminum-doped magnetite nanoparticles are producedby the process comprising: dissolving stoichiometric amounts of ferricsalt, ferrous salt, and aluminum salt in a fluid to form a solution; andincreasing the pH of the solution using a basic solution including oneor both sodium hydroxide and ammonium hydroxide until precipitation ofthe solid solution aluminum-doped magnetite nanoparticles.
 11. Themethod of claim 10, wherein the process of producing the solid solutionaluminum-doped magnetite nanoparticles further comprises: heating thesolution prior to increasing the pH of the solution; and heating thesolution during increasing the pH of the solution.
 12. The method ofclaim 10, wherein the ferric salt, ferrous salt, and aluminum saltcomprise Al₂(SO₄)₃, FeCl₃, and FeCl₂; wherein increasing the pH of thesolution comprises increasing the pH of the solution with the additionof one or both of NaOH and NH₄OH; and wherein the solid solutionaluminum-doped magnetite nanoparticles comprise 20 to 50% aluminum. 13.A method comprising: forming contaminate-adsorbed nanoparticles byintroducing solid solution aluminum-doped magnetite nanoparticles havinga magnetite structure with aluminum fully incorporated in the cubicinverse spinel lattice of the magnetite structure to a fluid with acontaminate selected from the group consisting of biochemical oxygendemand (BOD), chemical oxygen demand (COD), total suspended solids(TSS), total dissolved solids (TDS), fat-oil-grease (FOG), totalKjeldahl nitrogen (TKN), suspended solids, dissolved solids, and acombination thereof; isolating at least a portion of thecontaminate-adsorbed nanoparticles by applying a magnetic field to thefluid; removing at least a portion of the isolated contaminate-adsorbednanoparticles from the fluid; and regenerating with an aluminum solutionat least a portion of the removed contaminate-adsorbed nanoparticlesinto regenerated solid solution aluminum-doped magnetite nanoparticles;wherein the solid solution aluminum-doped magnetite nanoparticles arecharacterized by a maximum contaminate adsorption capacity of greaterthan 50 mg/g based on the Langmuir model; wherein the solid solutionaluminum-doped magnetite nanoparticles prior to regenerating have aninitial contaminate removal efficacy; and wherein the regenerated solidsolution aluminum-doped magnetite nanoparticles are configured such thatafter the same solid solution aluminum-doped magnetite nanoparticleshave been regenerated up through 11 cycles of being regenerated, thecycled regenerated solid solution aluminum-doped magnetite nanoparticleshave a regenerated contaminate removal efficacy that is at least 70% ofthe initial contaminate removal efficacy.
 14. The method of claim 13,wherein an isolation efficiency of the contaminate-adsorbednanoparticles is pH-independent in the range of the fluid pH from 4 to9.
 15. The method of claim 13, wherein the solid solution aluminum-dopedmagnetite nanoparticles are synthesized from a mixture of ferric salt,ferrous salt, and aluminum salt with sodium hydroxide; and wherein thesolid solution aluminum-doped magnetite nanoparticles are characterizedby a maximum contaminate adsorption capacity of greater than 81 mg/gbased on the Langmuir model.
 16. The method of claim 13, wherein thesolid solution aluminum-doped magnetite nanoparticles are characterizedby a maximum contaminate adsorption capacity of greater than 102 mg/gbased on the Langmuir model.
 17. The method of claim 13, wherein acontainment concentration of the fluid after removal of at least aportion of the isolated contaminate-adsorbed nanoparticles is from about40% to about 97% less than a containment concentration of the fluidprior to forming the contaminate-adsorbed nanoparticles.
 18. The methodof claim 13, wherein the solid solution aluminum-doped magnetitenanoparticles are produced by the process comprising: dissolvingstoichiometric amounts of ferric salt, ferrous salt, and aluminum saltin a fluid to form a solution; and increasing the pH of the solutionusing a basic solution including one or both sodium hydroxide andammonium hydroxide until precipitation of the solid solutionaluminum-doped magnetite nanoparticles.
 19. The method of claim 18,wherein the process of producing the solid solution aluminum-dopedmagnetite nanoparticles further comprises: heating the solution prior toincreasing the pH of the solution; and heating the solution duringincreasing the pH of the solution.
 20. The method of claim 18, whereinthe ferric salt, ferrous salt, and aluminum salt comprise Al₂(SO₄)₃,FeCl₃, and FeCl₂; wherein increasing the pH of the solution comprisesincreasing the pH of the solution with the addition of one or both ofNaOH and NH₄OH; and wherein the solid solution aluminum-doped magnetitenanoparticles comprise 20 to 50% aluminum.